If we stare at a distant star like Alpha Centauri for example, we are technically looking four years in the past (because light travelling at light speed will take that long to reach our eyes). Let us imagine that we somehow stumble upon a wormhole big enough to fly a starship through and travel to a planet, say, a hundred light years away in a few hours. Now...if we had a telescope powerful enough, and aimed it at Earth, would we then see planet Earth 100 years in the past? If so, would that be some kind of paradox? Is that time travel? Is it possible? I know that theoretically wormholes are possible, and maybe even travel between them, but stuff like this seems like a major hickup in the universe. Now I know that you're gonna say that no telescope is powerful enough to see any detail of Earth from 100 LY away, humor me, the essence would be the same. I thank you now Cogito and Wreybies, because more than likely you guys will be the first to respond to this thread. Whenever heavy nerd SF talk is in the air you guys always seem to sniff it out somehow.
I'll surprise you, Jonathan, and get here before the other two. (And I didn't need time travel or any wormhole to achieve it) You're absolutely correct of course. If you look at anything 100 light years away, then you're seeing light that left it 100 years ago, therefore seeing it as it was 100 years earlier. So, if you travel through a wormhole that could take you 100 light years in a few hours (or days, or months, or even years), then you could, in theory, with a powerful enough telescope, watch your long-dead grandfather mowing his lawn. Mind-boggling stuff, to be sure!
Ha! I don't think it would constitute a paradox because the light that you are looking at coming from the Earth would just be old light. Old information. It would be infinitely interesting, though, were you able to bring such a thought experiment to fruition and have the capacity to see Earth from your proposed 100-light-years-away-star with some kind of detail. It would give you a veritable window into the past.
Wow thats reallly really amazing. I had always known that the stars we look at are years old and we are seeing something of the past. The stars we are looking at might not even be there anymore. Well I think, dunno. But the concept of looking at Earth like that would be... well amazing. Would be interesting to see this used in a book.
Yes, but it isn't really a paradox... Here's another strange thing though, apparently if you travel faster than the speed of light from points A to B, supposedly the distance between these two points will decrease as you do so... never made much sense to me... correct me if I'm wrong anyone.
Thanks guys for the response, I love talking about this stuff! I love the way real science opens up conversations like these and creates ideas for stories. Even if we can't travel to the past, the idea of being able to see it excits me to no end. If only I could see the Hanging Garden of Babylon in it's golden age Oh and Mantha, I have thought about that as well, if we were to accelerate towards a star system at FTL speeds in theory we should be seeing time go in reverse, which is also mind-boggling. I just did not dare mention it, FTL travel violates Einstein's laws and is near hersey in science, but makes SF so much more enjoyable! It might be possible that our children's children in the 25th century are watching the tops of our heads now from a distant star
This is not so easy. Time travel is not a precise word. I would say no, because you see the earth as has been experienced on earth 100 years before your lift-off, but you only see "old" light. Interesting however -- how would you see earth looking in the rear-view mirror of your portable wormhole? Like a quick reverse? 100 years backwards in 3 seconds? 2) possible? may be not an exactly pleasant experience to be mangled through a wormhole but -- who knows. 3) Check on Einsteins twink paradox, also might give you some inspiration. (Very roughly, everyone has got their own frame of reference, concerning space and time, so if you travel away from the earth, accelerating close to the speed of light, turning round *brakes screeching, you come back and find your imaginary twin has aged more than you have.) (Also check on "time dilatation") And -- if you want it to get really mind-boggling timewarpingly awful, go to quantum level and add tunnel effects to the mix. Or a little probability field stuff from Richard P. Feynman.
The size of "you" matters here. If you are a sub-atomic particle, quantum laws apply. You are an electron, e.g., mostly going oround some atomic core on different energy levels roughly described by Bohr. According to quantum theory these energy levels -- the shells of the atom model -- are only the places with the biggest chance to encounter the particle. But there is a very small probabilty that the particle may be not there, but anywhere really. So the tunnel effect -- correct me if I'm wrong -- describes a particle suddenly appearing at one spot, seemingly leaping there from another, without ever having passed through whatever was between the two spots. So that defies the rule of "nothing can travel faster than the speed of light" somehow. The space not really shrinks between the two spots, but then .. maybe there is an explanation involving curvature of spacetime ... Though I doubt it, if you manage to mix relativisic and quantum stuff in a meaningful way you are in for the Nobel Prize. (Only works on the sub-atomic scale though, over really small distances. Fat chance of your mother-in-law suddenly materializing through your bedroom wall, luckily.)
Your questions have already been answered, but I thought I'd throw in my 2 cents. Another aspect of relativity that most people don't usually understand is that as you approach light speed, time slows down for you. Most assume that if something is 1,000 light years away, that you would age 1,000 years on the journey. But in fact, the trip would be almost instantaneous to you. Heck, you could travel from one end of the universe to the other instantaneously. Another interesting thing about this is that since your spacecraft's computer is also subject to time dilation, it might not be able to tell the engines to stop in time to get to your destination. For the time it takes the electrons to get from the CPU to the switch that kills your engines, you might have overshot Alpha Centauri by a several tens of billions of light years...just in time to witness the death of the universe. Most scientists consider this time travel. So, yes, forward time travel is possible.
Seen from a casual observer on earth -- firmly grounded in his own frame of reference -- you still wouldn't be accelerating to anything faster than the speed of light. But you are right. This "continuinuinuum stuff" (Pratchett) is just awesome, isn't it?
Oh wow! This thread my have just converted me to SF - I was never interested in the stuff, but now I am. Now, I don't know anything about this, but some of you really sound like you know your stuff and I want to say: Thanks for sharing! Are you saying that if a planet disappeared, we wouldn't know about it for many years even though we are watching the planets all the time? What about if it was the sun? If the sun just went away (not saying its a possiblity), we would have no idea until many years later? What about the moon? We see the moon every night is it really where we see it? Or is the moon too close? Or am I not getting this at all? Lets assume there is life on another planet and they have the means to look at us; they may know our past better then we do; right? They would be far better informed then us, since we only know our history from books written by 'someone' and they can see it now?
The sun is about 8 light-minutes away from us -- if my memory doesn't fail me on this -- so if somebody snatched it, you wouldn't know until 8 minutes later. Wait, now I am interested c= 299 792 458 meters per second ... just looked it up. the distance earth -- moon is roughly 384 400 000 m, it varies a bit the distance earth -- sun is roughly 150 million km, that is .. er ... 150 000 000 000 m so: light travels the distance moon - earth in ... 1.2 seconds light travels the distance sun - earth in ... 500 seconds, equals roughly 8 minutes If i missed a zero somewhere, anyone correct me on this xD Absolutely right. For them, the drawback concerning this is ... They have no means to tell what we are doing just now, because any information would travel at the speed of light to them, but not any faster. So they will find out in x years. (Hmm I got an idea ... Let us surprise them and do some weird stuff... Rearranging some mountains to form rude symbols that can only be seen from space.. or something xD)
Meliha. Light travels at 186,000 miles per second. Not much less than the average distance between the Earth and the Moon. Therefore, we'd know about something catastrophic happening to the moon in only a second or so.
Hahaha... wow, that's a relief! I was already thinking 'My God! we could be running out of sunlight and here I am worrying about loans and health and what-not' Lankin, thank you so much!!! I think I'm going to write a comedy piece on this - 8 minutes for a doofus to save the sun and hence the planet; heck (in for a penny in for a pound - as they say) he needs to save the whole galaxy. If I ever get it published you can be sure I will mention your contribution - thanks again
Meliha, you don't read SF??? you need to read some of the classics right now young lady! I suggest you start with the grand masters like Asimov, Clarke, and Heinlein Larry Niven wrote a story called "Inconstant Moon" that got turned into an Outer Limits show. The MC was observing something brilliant on the Moon, made some calculations, and concluded that something horrible happened to the sun, like a nova, and the Moon's albedo caught the light and reflected it. He deduced (because it was night time there) that the sun-faced side had been scorched and that it was only a matter of time, as the Earth rotated, before he would die. It turned out to be a great solar flare and if memory serves me correctly he survived, but there was widespread global damage.:redface: Fusion power kicks butt.
the thing about light speed is this...you may be able to travel to 99.9% of the speed of light, but the moment you hit the speed of light, your weight becomes infinite. meaning that you wouldn't be able to move at all. Actually, you'd burst apart. Einstein has shown this and science has proven this with hadron colliders and such. The next thing you have to see, is most scientists consider a wormhole to be a travel through time, not through the empty reaches of space. Think of time as a plane, everything on it moves time around. When a wormhole comes into play, that plane is bent over itself. When you use a wormhole, you are actually traveling, backward or forward through time in the same spot you entered from. Thus, allowing you to travel through time. Now what you are really looking for is a ship with a warp drive that can distort time and space in front of you, squeezing it together and pushing it out behind you in its non-distorted form. Basically making time and space move, but not yourself. You don't break any laws of relativity in this approach, or with the time travel. If only we had the technology to produce any of these most used scientific theories. But in the original question, yes you'd be able to see the light from earth as it stood a hundred years ago. However, if you are that far away, earth would give no light, it would actually be our sun that you saw. In fact it would be hard pressed for you to even see anything of earth from the distance you are talking about. Stars give us the light we see in the night sky, (Or the reflection of our closest planets) not planets themselves. The reflection from earth would dissipate over that long of a travel.
Your memory doesn't fail you This is really interesting discussion. Regarding SF, I don't know why--I love SF movies but never really liked SF novels. So, suggest some good SF novels and convert me!!
Gonna correct you here. That's not exactly what happens. As you approach the speed of light, your mass approaches infinity. The more mass you have, the more energy you need to speed up. Eventually you get to a point where all the energy in the universe couldn't speed you up any faster. That's why the speed of light is the limit. But that's only if you have a non-zero rest mass. If you have a zero rest mass, you can only travel at the speed of light. If you have a negative rest mass... well, let's say it gets a whole lot weirder. Units like this make physicists cry. Trust me, I am one. It's much easier to remember that it goes at 300,000,000 metres per second (approximately). Much nicer number and metres are a better unit.
Almost correct. In truth, you approach that point more and more closely, but you never actually reach it. However, we'll accept the answer as acceptable in a finite universe. And real physicists don't fear numeric conversions. Real physicists can use computers.
I have found that working in the metric system is much much easier for me to make calculations. Whenever I do quick mental divisions and stuff I'm like, duh? Metric system? Ten times/multiplied by ten a few times? And then there's scientific notations, it's so easy to multiply using them, just add zeroes, easy as pie, and it boggles peoples' minds IMO, if you can reach 99.9% the speed of light, it's almost as good just like we can never reach absolute zero, but get within a trillionth of a degree of it
0.999 C is ok for the passengers on the ship, as long as they don't have any family they want to stay in touch with back home. Shipboard time is compressed, and the distance to the destination shrinks. So yes, it can take considerably less than ten years of shipboard time to reach a star ten light years away, but it will be more than ten years from an external observer on the source or destination planet. Increase the flight distance to 100 light years, and the goodbye is permanent. All this is based on accelerating to 0.999 C quickly, and decellerating equally quickly, so most of the flight takes place at 0.999 C. But don't accelerate so quickly you crush your passengers...
